Showing papers in "Opto-electronics Review in 2003"

HgCdTe epilayers on GaAs: growth and devices

Abstract: View of basic and specific physical and chemical features of growth and defect formation in mercury cadmium telluride (MCT) heterostructures (HS's) on GaAs substrates by molecular beam epitaxy (MBE) was made. On the basis of this knowledge a new generation of ultra high vacuum set, ultra-fast ellipsometer of high accuracy and automatic system for control of technological processes was produced for reproducibility of MCT Hs's growth on substrates up to 4" in diameter. The development of industrially oriented technolgoy of MCT HS's growth by MBE on GaAs substrates 2" in diameter and without intentional doping is presented. The electrical characteristics of n-type and p-type of MCT HS's and uniformity of MCT composition over the surface area are excellent. The residual donor and acceptor centres are supposed as hypothetically tellurium atoms in metallic sublattice ("antisite" tellurium) and double-ionised mercury vacancies. The technology of fabricating focal plane arrays is developed. The high quality characteristics of infrared detectors conductance and diode mode are measured. Calculations of detector parameters predicted the improvement in serial resistance and detectivity of infrared diode detectors based on MCT heterostructures with graded composition throughout the thickness.

Segmentation and feature extraction for reliable classification of microcalcifications in digital mammograms

Abstract: Microcalcifications are one of more important signs enabling detection of breast cancer at early stage. The main goal of the research was designing and realization of a system for automatic detection and classification of microcalcifications, taking advantage of proposed automatic feature selection algorithm. The first step of the detection algorithm is to segment the individual objects: potential microcalcifications. This is achieved by applying opening by reconstruction top-hat technique and image thresholding based on approximation of an image local histogram with a probability density function of Gauss distribution. Selected features of the segmented objects are used as inputs to neural networks. The first classifier verifies the initial detection and the others assess a diagnosis of the input objects. The algorithm results are locations of suggested microcalcifications and optionally automatic diagnosis. The presented form of the system was verified in clinical tests using diagnosed databases (DDSM from University of South Florida and own digitized database of mammograms ). Achieved results are promising, comparable with other known systems. Efficiency of microcalcifications detection was up to 90%.

Multichannel capacitance tomograph for dynamic process imaging

Abstract: Electrical capacitance tomography (ECT) is a useful tool for dynamic processes imaging in research and industry. Capacitance tomography provides three-dimensional information about the process. This knowledge enables improved monitoring and control of the processes. Capacitance tomography is one of the techniques, which have been primary developed for the process technology. It is low cost, high speed, robust and non-invasive. Electrical capacitance tomography is a technique, which aims to image electrical permittivity distribution in a volume enclosed in measuring electrodes. The paper describes an ET2 capacitance tomograph designed and developed at the laboratory of the Institute of Radioelectronics. The tomograph was elaborated in collaboration with the Industrial Institute of Organic Chemistry and will be used for research works performed by that institute. Like other ECT systems, the ET2 consists of three units, a sensor, a sensing electronics, and a computer. The ET2 system can work with 8-, 12-, 16or 32electrode capacitance probe. The measurement and processing module is an electronic circuitry, containing a set of PCB boards, installed in a separate housing (19-inch wide “Eurocase”), together with a dedicated power supplier and a communication port. A PC-compatible computer controls a measurement process, provides image reconstruction, presentation, and interpretation.

Face detection in colour images using fuzzy Hough transform

Abstract: Novel, fast, accurate, and low complexity face localisation algorithm is presented. It is robust for hard scene conditions, such as complex background, different lighting, and face poses. It exploits spatial masking of face colour areas in normalised perceptually plausible tint-saturation-luminance (TSL) space where Canny filter is applied. Then, facial areas are approximated by ellipses of constrained proportions using fuzzy Hough transform on detected edges. Finally eye localisation technique is applied in Cr-Cb colour space in order to determine face pose, confirm face presence, and it enables us normalisation of face recognition.

Information theory based medical images processing

Abstract: Increasing application of non-invasive medical techniques (like stereotactic radiosurgery) generates a high demand for modern image processing algorithms Image registration and segmentation are the two essential examples of this The algorithms need to be reasonably fast, reliable, accurate, and highly automated Information theory provides a means to create such systems In this paper we present thresholding segmentation using image entropy and a registration technique based on maximization of mutual information Then we show some experimental results using real-world computed tomography (CT) and medical resonance imaging (MRI) data

Fully self-consistent three-dimensional model of edge emitting nitride diode lasers

Abstract: A comprehensive, fully self-consistent, optical-electrical-thermal-gain, three-dimensional model of edge-emitting (EE) nitride diode lasers has been developed and used to simulate a room-temperature (RT) continuous-wave (CW) threshold operation of typical EE designs of a nitride diode laser. With the aid of the model, some RT CW performance characteristics of the laser have been anticipated taking into consideration important features of nitride materials. These features have proved already to be often essentially different from those of other AIIIBV materials, therefore expected properties of nitride devices cannot be estimated on the basis of known properties of analogous devices manufactured from other materials.

Status of HgCdTe photodiodes at the Military University of Technology

Abstract: The paper presents technological achievements in fabrication of cryogenically-cooled and ambient temperature HgCdTe photodiodes carried out during the last four years at the Institute of Applied Physics, Military University of Technology. Because of the complicated and expensive fabrication process, numerical simulation has become a critical tool for the development of HgCdTe bandgap engineering devices. Therefore in the second part of the paper, an original iteration scheme is used to predict the effect of composition and doping profiles on the heterojunction detector parameters. A novel tipping boat for liquid phase epitaxial (LPE) growth of HgCdTe from Te-rich solutions has been proposed. The successful fabrication of long wavelength infrared (LWIR) Hg1nyCdyTe/Hg1nxCdxTe heterostructures (y > x) on semi-insulating (111)CdZnTe substrates is presented. The performance of p-on-n double-layer heterojunction (DLHJ) photodiodes at temperature 77 K is analysed. It is also shown that LPE can be used to realise advanced bandgap engineered multi-junction structures. The parameters and characteristics of the new type of HgCdTe buried photodiodes, operated at near-room temperature (T = 200n300 K) in LWIR spectral range, are reported. Finally, an effective numerical model for performance predictions of HgCdTe heterostructure device is presented. The model is used to analyse the performance of dual-band HgCdTe photovoltaic detector and mid wavelength infrared (MWIR) HgCdTe heterostructure device. In the last case, it is shown that excess 1/f noise of MWIR non-equilibrium heterostructure device is connected with fluctuation of carrier mobility.

Colour temperature estimation algorithm for digital images-properties and convergence

Abstract: The paper presents an algorithm for estimation of temperature of image. Colour temperature is important, perceptual feature describing colour and content of images. The main idea of the algorithm is to average pixel values of image, omitting the values which have meaningless influence on perception of colour temperature. It is done in an iterative procedure. The convergence of the procedure is discussed. The algorithm can be applied in image search/retrieval tasks and is proposed in the MPEG-7 colour temperature descriptor for estimation of colour temperature of images.

New mid-infrared optical sources based on isotropic semiconductors (zinc selenide and gallium arsenide) using total internal reflection quasi-phase-matching

Abstract: The French aerospace agency is involved in the realization of compact solid-state coherent sources, such as optical parametric oscillators (OPO), using new materials, such as highly non-linearly efficient semiconductors (ZnSe, GaAs or InP). However, since these materials are optically isotropic, they require new phase-matching techniques. We report the quasi-phase matched difference frequency generation in isotropic semiconductors using total internal reflection. We made use of large Fresnel birefringence at reflection between the signal and idler wave outputs of an OPO. Large tunability (between 8 and 13 μm) is demonstrated. Agreement between theoretical expectation and experimental results is excellent.© (2003) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Analysis of VLWIR HgCdTe photodiode performance

Abstract: The performance of very long wavelength infrared (VLWIR) HgCdTe photodiodes at temperatures ranging from 77 K up to 150 K is presented. The effect of inherent and excess current mechanisms on quantum efficiency and dynamic resistance-area RA product is analysed. Different methods of determining the ideality factor are shown and among them the one based on the use of RA product versus bias voltage proves to be the most reliable. At higher temperatures, however, the calculated ideality factor does not give any useful information about the nature of the p-n junction current due to significant influence of the series and shunt resistances. A comparison of the experimental data with the results of analytical and numerical calculations shows that the photodiodes with cut-off wavelength up to 14.5 μm are diffusion-limited at temperatures exceeding 100 K.

Multilayer strained Si-SiGe structures: fabrication problems, interface characteristics, and physical properties

Abstract: The objectives of this investigation are structural and physical characteristics of the n-Si1-xGex/n(p)-Si heterojunction under strong elastic deformation of Si1-xGex layers which gives rise to misfit dislocations in the heteroboundary region; the factors playing the main role in formation of the band structure of the system; the use of transmission electron microscopy and optical methods for determination of the phenomena connected with misfit dislocations in the grown epitaxial structure; the electrical characteristics of diode structures and the process of electron-hole recombination via dislocation states in a heterojunction.© (2003) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Spectral detectivity and NETD of doping-spike PtSi-p-Si and HIP GeSi-Si detectors

Abstract: Platinum silicide Schottky barrier detectors (SBD) and HIP-detectors GeSi/Si-based are widely used for application in the infrared spectral range. The increase in cutoff wavelength and responsivity of PtSi-Si photodevices is possible by formation of heavily-doped thin layer near to the semiconductor surface. The cutoff wavelength of HIP-detectors GexSi1-x/Si-based depends on x and concentration of boron in GeSi. In this report, the threshold properties of these detectors are considered. The dependencies of spectral detectivities and NETD from cutoff wavelength are calculated for various parameters of SBD and HIP-detectors. It is shown that optimal NETD of a SBD and HIP-detectors is possible for certain cutoff wavelength and temperature of detectors and depends on storage capacity. Also opportunity of formation of heavily-doped nanolayer in SBD detectors used by short-pulse recoil implanation of boron was studied.© (2003) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

A super-resolution method based on signal fragmentation

Abstract: General idea of the super-resolution method based on the signal-spectrum extrapolation beyond transmission-channel band has been presented. Main limitations of former realizations of the method have been discussed. A new realization procedure of the method, removing those limitations, has been proposed. It consists in signal fragmentation before transmission through a low-pass channel. Results of a few numerical experiments done by means of original computing tools has been presented and discussed.

Kinetics of photoluminescence of porous silicon studied by photo-luminescence excitation spectroscopy and time-resolved spectroscopy

Abstract: Photoluminescence (PL) spectra and excitation spectra (PLE) (under steady-state conditions), time resolved spectra (PL-TRS) and decay curves of photoluminescence (PL-DC) in micro- and nanosecond range (under pulsed operation) at different temperatures (10 K-room) on anodically etched boron-doped silicon are presented. PLE shows that visible PL is excited by light from UV region. PL and PL-TRS exhibit multiband structure and can be decomposed as a sum of few Gaussians. PL-DCs have multiexponential shape. Relaxation times depend on wavelength of the observation. To explain our results we assumed a model in which the multibarrier structure is formed by larger Si crystallites or wires (quantum well) surrounded by Si crystallites with diameters in the nanometer range (barrier region). The visible photoluminescence originates from radiative recombination between discrete energy levels in a quantum well.© (2003) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.